Good day, Vlad!
Would you help me with a problem with the menu? The matter is that I can see all section of submenu on the main page, but should I go to some page, the last item is not displayed. It seems that the length of the submenu is bounded the size of the image.

Small issue there. Go to Appearance > Editor and navigate at the bottom of the file that opens automatically.
Add this code at the bottom:

.site-header {
   overflow: visible;

Got it! Works well, many thanks!